Can we please differentiate GPT from EFI. GPT may be part of the EFI specification, but it's a standalone piece - implementing GPT is not going to restrict anyone's freedom to do what they want with a machine. Some possibilities EFI offers are more contentious..
GPT is a foregone conclusion unless you are blind to the future. The only alternative is OS specific disk hackery, and that does no-one any favours. Single disk 2TB+ partitions will not even attract comment inside the next 5 years. Several operating systems out there can happily read GPT disks using a non EFI BIOS (provided it's not necessary to boot from it), and even in the case where it's a GPT disk with a GPT only OS (i.e OS X Intel) on a non EFI BIOS, there are workarounds to get it to boot. Of course, it isn't /quite/ that simple. GPT is still fairly new, and whilst it's not too difficult to get a number of operating systems to boot from GPT, sharing a disk has a number of gotchas. Google is your friend for details here. I can also say, having done it (and the fact it's not easily googleable) that although 'hybrid GPTs' (a GPT disk where the protective fake MBR is hacked to become a real MBR) are frowned upon (there is potential for breakage) it does work and it's even possible to hack in an extended partition (OpenBSD's Fdisk is much better than the alternatives for doing this piece of hackery). It's entirely possible to get a disk sharing OpenBSD, NetBSD, Linux, Vista Windows 7 and OS X without any of them overwriting data from the others. Just be careful. (for clarity, OS X was the only OS using a real GPT partition : everything else was on MBR, despite the fact that Windows 7/Vista SP2 x64 (not 32bit), Linux and NetBSD will boot from GPT partitions with appropriate hackery. Note that IIRC vanilla NetBSD 5.x will need a customised kernel to run from a hybrid MBR on GPT, otherwise it gets confused by the presence of a GPT header. The boot loader was the hackintosh chameleon with Windows 7's partition manager as a slave (very flexible once you get to know it. Use easyBCD))
